1. Field of the Invention
The present invention relates to an infrared radiation image detector for detecting infrared radiation radiated from a material as image data and, more particularly, to improvements in the structure of a cryogenic container with a sensing element disposed thereto.
2. Description of the Prior Art
A sensing element for sensing infrared radiation, which takes advantage of Schottkey joints of semi-conductor silicon, is so low in a joint barrier that operations at room temperature are difficult and that the operations should be conducted at cryogenic temperatures, i.e. at the temperature of liquid nitrogen of approximately 80K, in order to remove outside turbulence of temperature. Hence, a main body of the sensing element is disposed to a container having special structure as capable of cooling the sensing element at cryogenic temperatures and having an infrared radiation-transmitting window mounted thereto.
FIG. 3 shows the structure of an infrared radiation detector of a type as disclosed, for example, in Japanese Patent Laid-open Publication (kokai) No. 2-214,158. The infrared radiation detector contains a cryogenic container comprising an outer cylinder 3 with a window member 2 joined air-tight thereto, through which entering infrared radiation 1 passes, and an inner cylinder 4 connected integrally to the outer cylinder 3 and having a space 13 with the inside sealed and held at vacuo. To a top end portion 4a of the inner cylinder 4 of the cryogenic container is mounted the sensing element 10 for detecting infrared radiation generated from a semi-conductor through a sub-package 11 consisting of a frame-shaped package and a package bottom plate. At a top portion of the sub-package 11 is mounted a peripheral wall 12 for blocking stray light of entering infrared radiation 1, as called a cold shield, and an electric signal from the sensing element 10 is generally fetched into the outside of the cryogenic container with the aid of a terminal 5 of a glass hermetic seal 6 disposed at an outer cylindrical portion through an inner wire 8 along a side wall of the inner cylinder 4 via a terminal of the sub-package 11.
Description will now be made of the operations of the infrared radiation detector with reference to FIG. 3. As shown in FIG. 3, the infrared radiation 1 entering the cryogenic container through the infrared radiation-transmitting window 2 forms an image on a rear surface of the sensing element 10, and an electric charge carrier is produced in accordance with the magnitude of infrared rays. The electric charge is read by an electric charge transmitting section (not shown) integrated in the identical element and displayed as image data on an external signal processing circuit (not shown) through a non-illustrated package leads and inner cryogenic container leads 8 and an external terminal 5. During the operations of the detector, a cooling device, such as of a Joule-Thomson type or of a closed cycle type or the like, is inserted into a space 14 of the cryogenic container, and the sensing element 10 is cooled to the 80K level through the top end portion 4a of the inner cylinder 4 of the cryogenic container.
From the structure and operations of the infrared radiation detector as described hereinabove, the image signal of the sensing element for detecting infrared rays is processed as image data by the signal processing circuit disposed outside the cryogenic container. In this case, it is desired that the length of the lead within the cryogenic container be shortened to the shortest possible level in order to prevent deterioration of wave forms of signals detected. If the number of matrix pixels of the sensing element is increased in order to improve the dissolution of image data, it is necessary to increase the number of leads for fetching signals and to increase the density of the leads disposed on the wall surface of the inner cylinder and the number of external terminals of the hermetic seal of the outer cylinder of the cryogenic container.
In the structure of the conventional cryogenic container as shown in FIG. 3, the length of the lead is forced to be prolonged because the inner lead 8 is connected through the wall surface of the inner cylinder 4 to the terminal 5 disposed underneath the outer cylinder 3. The inner diameters of the inner cylinder 4 and the outer cylinder 3 of the cryogenic container are delimited by an interface with other parts relating to the infrared radiation detector, so that limitations are placed upon making the inner leads highly dense and increasing the number of the external terminals.
In summary, the conventional infrared radiation detector presents the drawbacks that there are limitations on prolonging the length of the internal leads of the cryogenic container, making the internal leads highly dense, and increasing the number of external terminals.